Due to the limited hydrofluoric (HF) acid budget that a typical semiconductor-on-insulator (SOI) based transistor fabrication process entails, in the case of a thin buried oxide (BOX) the substrate may be exposed either fully or in part at the divot, particularly with Ultra-Thin Body and BOX (UTBB) substrates. This can cause SOI/substrate shorts through a misaligned contact going over the shallow trench isolation (STI) and connecting the source/drain (S/D) with the substrate. Because of the thin BOX, the contact etch has very marginal room.
There is, therefore, a need in the art for improved protection against shorts from a source/drain region to the substrate due to penetration of misaligned contacts through the buried oxide.